Dinitrogen Complexes of Cobalt(-I) Supported by Rare-Earth Metal-Based Metalloligands.

Sequential reactions of heptadentate phosphinoamine LH 3 with rare-earth metal tris-alkyl precursor (Me 3 SiCH 2 ) 3 Ln(THF) 2 (Ln = Sc, Lu, Yb, Y, Gd) and a low-valent cobalt complex (Ph 3 P) 3 CoI afforded rare-earth metal-supported cobalt iodide complexes. Reduction of these iodide complexes under N 2 allowed the isolation of the first series of dinitrogen complexes of Co(-I) featuring dative Co(-I) → Ln (Ln = Sc, Lu, Yb, Y, Gd) bonding interactions. These compounds were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The correlation of N-N vibrational frequencies with the p K a of [Ln(H 2 O) 6 ] 3+ showed that strongest activation of N 2 was achieved with the least Lewis acidic Gd(III) ion. Interestingly, these Ln-Co-N 2 complexes catalyzed silylation of N 2 in the presence of KC 8 and Me 3 SiCl with turnover numbers (TONs) up to 16, where the lutetium-supported Co(-I) complex showed the highest activity within the series. The role of the Lewis acidic Ln(III) was crucial to achieve catalytic turnovers and tunable reactivity toward N 2 functionalization.